busybox/loginutils/login.c

/* vi: set sw=4 ts=4: */
/*
 * Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
 */

#include <fcntl.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <syslog.h>
#include <termios.h>
#include <unistd.h>
#include <utmp.h>
#include <sys/resource.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <ctype.h>
#include <time.h>

#include "busybox.h"
#ifdef CONFIG_SELINUX
#include <selinux/selinux.h>  /* for is_selinux_enabled()  */
#include <selinux/get_context_list.h> /* for get_default_context() */
#include <selinux/flask.h> /* for security class definitions  */
#include <errno.h>
#endif

#ifdef CONFIG_FEATURE_UTMP
// import from utmp.c
static void checkutmp(int picky);
static void setutmp(const char *name, const char *line);
/* Stuff global to this file */
static struct utmp utent;
#endif

enum {
	TIMEOUT = 60,
	EMPTY_USERNAME_COUNT = 10,
	USERNAME_SIZE = 32,
};

static int check_nologin(int amroot);

#if defined CONFIG_FEATURE_SECURETTY
static int check_tty(const char *tty);

#else
static inline int check_tty(const char *tty) { return 1; }

#endif

static int is_my_tty(const char *tty);
static int login_prompt(char *buf_name);
static void motd(void);


static void alarm_handler(int sig ATTRIBUTE_UNUSED)
{
	fprintf(stderr, "\r\nLogin timed out after %s seconds\r\n", TIMEOUT);
	exit(EXIT_SUCCESS);
}


int login_main(int argc, char **argv)
{
	char tty[BUFSIZ];
	char full_tty[200];
	char fromhost[512];
	char username[USERNAME_SIZE];
	const char *tmp;
	int amroot;
	int flag;
	int failed;
	int count = 0;
	struct passwd *pw, pw_copy;
#ifdef CONFIG_WHEEL_GROUP
	struct group *grp;
#endif
	int opt_preserve = 0;
	int opt_fflag = 0;
	char *opt_host = 0;
	int alarmstarted = 0;
#ifdef CONFIG_SELINUX
	security_context_t user_sid = NULL;
#endif

	username[0] = '\0';
	amroot = (getuid() == 0);
	signal(SIGALRM, alarm_handler);
	alarm(TIMEOUT);
	alarmstarted = 1;

	while ((flag = getopt(argc, argv, "f:h:p")) != EOF) {
		switch (flag) {
		case 'p':
			opt_preserve = 1;
			break;
		case 'f':
			/*
			 * username must be a separate token
			 * (-f root, *NOT* -froot). --marekm
			 */
			if (optarg != argv[optind-1])
				bb_show_usage();

			if (!amroot)		/* Auth bypass only if real UID is zero */
				bb_error_msg_and_die("-f permission denied");

			safe_strncpy(username, optarg, USERNAME_SIZE);
			opt_fflag = 1;
			break;
		case 'h':
			opt_host = optarg;
			break;
		default:
			bb_show_usage();
		}
	}

	if (optind < argc)             /* user from command line (getty) */
		safe_strncpy(username, argv[optind], USERNAME_SIZE);

	if (!isatty(0) || !isatty(1) || !isatty(2))
		return EXIT_FAILURE;		/* Must be a terminal */

#ifdef CONFIG_FEATURE_UTMP
	checkutmp(!amroot);
#endif

	tmp = ttyname(0);
	if (tmp && (strncmp(tmp, "/dev/", 5) == 0))
		safe_strncpy(tty, tmp + 5, sizeof(tty));
	else if (tmp && *tmp == '/')
		safe_strncpy(tty, tmp, sizeof(tty));
	else
		safe_strncpy(tty, "UNKNOWN", sizeof(tty));

#ifdef CONFIG_FEATURE_UTMP
	if (amroot)
		memset(utent.ut_host, 0, sizeof(utent.ut_host));
#endif

	if (opt_host) {
#ifdef CONFIG_FEATURE_UTMP
		safe_strncpy(utent.ut_host, opt_host, sizeof(utent.ut_host));
#endif
		snprintf(fromhost, sizeof(fromhost)-1, " on `%.100s' from "
					"`%.200s'", tty, opt_host);
	}
	else
		snprintf(fromhost, sizeof(fromhost)-1, " on `%.100s'", tty);

	bb_setpgrp;

	openlog(bb_applet_name, LOG_PID | LOG_CONS | LOG_NOWAIT, LOG_AUTH);

	while (1) {
		failed = 0;

		if (!username[0])
			if (!login_prompt(username))
				return EXIT_FAILURE;

		if (!alarmstarted && (TIMEOUT > 0)) {
			alarm(TIMEOUT);
			alarmstarted = 1;
		}

		pw = getpwnam(username);
		if (!pw) {
			pw_copy.pw_name   = "UNKNOWN";
			pw_copy.pw_passwd = "!";
			opt_fflag = 0;
			failed = 1;
		} else
			pw_copy = *pw;

		pw = &pw_copy;

		if ((pw->pw_passwd[0] == '!') || (pw->pw_passwd[0] == '*'))
			failed = 1;

		if (opt_fflag) {
			opt_fflag = 0;
			goto auth_ok;
		}

		if (!failed && (pw->pw_uid == 0) && (!check_tty(tty)))
			failed = 1;

		/* Don't check the password if password entry is empty (!) */
		if (!pw->pw_passwd[0])
			goto auth_ok;

		/* authorization takes place here */
		if (correct_password(pw))
			goto auth_ok;

		failed = 1;

auth_ok:
		if (!failed)
			break;

		bb_do_delay(FAIL_DELAY);
		puts("Login incorrect");
		username[0] = 0;
		if (++count == 3) {
			syslog(LOG_WARNING, "invalid password for `%s'%s", pw->pw_name, fromhost);
			return EXIT_FAILURE;
		}
	}

	alarm(0);
	if (check_nologin(pw->pw_uid == 0))
		return EXIT_FAILURE;

#ifdef CONFIG_FEATURE_UTMP
	setutmp(username, tty);
#endif

	if (*tty != '/')
		snprintf(full_tty, sizeof(full_tty)-1, "/dev/%s", tty);
	else
		safe_strncpy(full_tty, tty, sizeof(full_tty)-1);

#ifdef CONFIG_SELINUX
	if (is_selinux_enabled()) {
		security_context_t old_tty_sid, new_tty_sid;

		if (get_default_context(username, NULL, &user_sid)) {
			bb_error_msg_and_die("unable to get SID for %s",
					username);
		}
		if (getfilecon(full_tty, &old_tty_sid) < 0) {
			bb_perror_msg_and_die("getfilecon(%.100s) failed",
					full_tty);
		}
		if (security_compute_relabel(user_sid, old_tty_sid,
					SECCLASS_CHR_FILE, &new_tty_sid) != 0) {
			bb_perror_msg_and_die("security_change_sid(%.100s) failed",
					full_tty);
		}
		if (setfilecon(full_tty, new_tty_sid) != 0) {
			bb_perror_msg_and_die("chsid(%.100s, %s) failed",
					full_tty, new_tty_sid);
		}
	}
#endif
	if (!is_my_tty(full_tty))
		syslog(LOG_ERR, "unable to determine TTY name, got %s", full_tty);

	/* Try these, but don't complain if they fail
	 * (for example when the root fs is read only) */
	chown(full_tty, pw->pw_uid, pw->pw_gid);
	chmod(full_tty, 0600);

	if (ENABLE_LOGIN_SCRIPTS) {
		char *script = getenv("LOGIN_PRE_SUID_SCRIPT");
		if (script) {
			char *t_argv[2] = { script, NULL };
			switch (fork()) {
			case -1: break;
			case 0: /* child */
				xchdir("/");
				setenv("LOGIN_TTY", full_tty, 1);
				setenv("LOGIN_USER", pw->pw_name, 1);
				setenv("LOGIN_UID", utoa(pw->pw_uid), 1);
				setenv("LOGIN_GID", utoa(pw->pw_gid), 1);
				setenv("LOGIN_SHELL", pw->pw_shell, 1);
				execvp(script, t_argv);
				exit(1);
			default: /* parent */
				wait(NULL);
			}
		}
	}

	change_identity(pw);
	tmp = pw->pw_shell;
	if (!tmp || !*tmp)
		tmp = DEFAULT_SHELL;
	setup_environment(tmp, 1, !opt_preserve, pw);

	motd();
	signal(SIGALRM, SIG_DFL);	/* default alarm signal */

	if (pw->pw_uid == 0)
		syslog(LOG_INFO, "root login %s", fromhost);
#ifdef CONFIG_SELINUX
	/* well, a simple setexeccon() here would do the job as well,
	 * but let's play the game for now */
	set_current_security_context(user_sid);
#endif
	run_shell(tmp, 1, 0, 0);	/* exec the shell finally. */

	return EXIT_FAILURE;
}


static int login_prompt(char *buf_name)
{
	char buf[1024];
	char *sp, *ep;
	int i;

	for (i=0; i<EMPTY_USERNAME_COUNT; i++) {
		print_login_prompt();

		if (!fgets(buf, sizeof(buf)-1, stdin))
			return 0;

		if (!strchr(buf, '\n'))
			return 0;

		for (sp = buf; isspace(*sp); sp++) { }
		for (ep = sp; isgraph(*ep); ep++) { }

		*ep = '\0';
		safe_strncpy(buf_name, sp, USERNAME_SIZE);
		if (buf_name[0])
			return 1;
	}
	return 0;
}


static int check_nologin(int amroot)
{
	if (access(bb_path_nologin_file, F_OK) == 0) {
		FILE *fp;
		int c;

		fp = fopen(bb_path_nologin_file, "r");
		if (fp) {
			while ((c = getc(fp)) != EOF)
				putchar((c=='\n') ? '\r' : c);

			fflush(stdout);
			fclose(fp);
		} else {
			puts("\r\nSystem closed for routine maintenance.\r");
		}
		if (!amroot)
			return 1;

		puts("\r\n[Disconnect bypassed -- root login allowed.]\r");
	}
	return 0;
}

#ifdef CONFIG_FEATURE_SECURETTY

static int check_tty(const char *tty)
{
	FILE *fp;
	int i;
	char buf[BUFSIZ];

	fp = fopen(bb_path_securetty_file, "r");
	if (fp) {
		while (fgets(buf, sizeof(buf)-1, fp)) {
			for(i = strlen(buf)-1; i>=0; --i) {
				if (!isspace(buf[i]))
					break;
			}
			buf[++i] = '\0';
			if ((buf[0]=='\0') || (buf[0]=='#'))
				continue;

			if (strcmp(buf, tty)== 0) {
				fclose(fp);
				return 1;
			}
		}
		fclose(fp);
		return 0;
	}
	/* A missing securetty file is not an error. */
	return 1;
}

#endif

/* returns 1 if true */
static int is_my_tty(const char *tty)
{
	struct stat by_name, by_fd;

	if (stat(tty, &by_name) || fstat(0, &by_fd))
		return 0;

	if (by_name.st_rdev != by_fd.st_rdev)
		return 0;
	else
		return 1;
}


static void motd(void)
{
	FILE *fp;
	int c;

	fp = fopen(bb_path_motd_file, "r");
	if (fp) {
		while ((c = getc(fp)) != EOF)
			putchar(c);
		fclose(fp);
	}
}


#ifdef CONFIG_FEATURE_UTMP
// vv  Taken from tinylogin utmp.c  vv

#define	NO_UTENT \
	"No utmp entry.  You must exec \"login\" from the lowest level \"sh\""
#define	NO_TTY \
	"Unable to determine your tty name."

/*
 * checkutmp - see if utmp file is correct for this process
 *
 *	System V is very picky about the contents of the utmp file
 *	and requires that a slot for the current process exist.
 *	The utmp file is scanned for an entry with the same process
 *	ID.  If no entry exists the process exits with a message.
 *
 *	The "picky" flag is for network and other logins that may
 *	use special flags.  It allows the pid checks to be overridden.
 *	This means that getty should never invoke login with any
 *	command line flags.
 */

static void checkutmp(int picky)
{
	char *line;
	struct utmp *ut;
	pid_t pid = getpid();

	setutent();

	/* First, try to find a valid utmp entry for this process.  */
	while ((ut = getutent()))
		if (ut->ut_pid == pid && ut->ut_line[0] && ut->ut_id[0] &&
			(ut->ut_type == LOGIN_PROCESS || ut->ut_type == USER_PROCESS))
			break;

	/* If there is one, just use it, otherwise create a new one.  */
	if (ut) {
		utent = *ut;
	} else {
		time_t t_tmp;
		
		if (picky) {
			puts(NO_UTENT);
			exit(1);
		}
		line = ttyname(0);
		if (!line) {
			puts(NO_TTY);
			exit(1);
		}
		if (strncmp(line, "/dev/", 5) == 0)
			line += 5;
		memset(&utent, 0, sizeof(utent));
		utent.ut_type = LOGIN_PROCESS;
		utent.ut_pid = pid;
		strncpy(utent.ut_line, line, sizeof(utent.ut_line));
		/* XXX - assumes /dev/tty?? */
		strncpy(utent.ut_id, utent.ut_line + 3, sizeof(utent.ut_id));
		strncpy(utent.ut_user, "LOGIN", sizeof(utent.ut_user));
		t_tmp = (time_t)utent.ut_time;
		time(&t_tmp);
	}
}

/*
 * setutmp - put a USER_PROCESS entry in the utmp file
 *
 *	setutmp changes the type of the current utmp entry to
 *	USER_PROCESS.  the wtmp file will be updated as well.
 */

static void setutmp(const char *name, const char *line ATTRIBUTE_UNUSED)
{
	time_t t_tmp = (time_t)utent.ut_time;

	utent.ut_type = USER_PROCESS;
	strncpy(utent.ut_user, name, sizeof(utent.ut_user));
	time(&t_tmp);
	/* other fields already filled in by checkutmp above */
	setutent();
	pututline(&utent);
	endutent();
#ifdef CONFIG_FEATURE_WTMP
	if (access(bb_path_wtmp_file, R_OK|W_OK) == -1) {
		close(creat(bb_path_wtmp_file, 0664));
	}
	updwtmp(bb_path_wtmp_file, &utent);
#endif
}
#endif /* CONFIG_FEATURE_UTMP */